This invention relates to a positive-working silicon-containing resist composition adapted to be exposed to radiations such as ultraviolet rays, far ultraviolet rays, X-rays, electron beams, molecular beams, xcex3-rays, and synchrotron rays. More particularly, it relates to a positive silicon-containing resist composition for micro-patterning which exhibits high resolution and high sensitivity to provide a resist having a rectangular profile with broad process latitude and is useful in the fabrication of semiconductor devices such as ICs, for example, in the fabrication of printed wiring boards.
A positive resist composition is used in, for example, processes comprising the steps of applying a positive resist composition to a substrate, such as a semiconductor wafer or a glass, ceramic or metal plate, either directly or via an antireflection coat or an organic coat by spin coating or roller coating to a thickness of 0.01 to 3 xcexcm, heat drying the applied composition to form a resist film, imagewise exposing the resist film through a photomask having a circuit or like pattern to active light rays, etc. developing the resist film to form a positive resist, and patternwise etching the substrate using the resist as a mask. Typical applications of a positive resist composition include fabrication of semiconductor devices, e.g., ICs, fabrication of circuit wiring boards for liquid crystals, thermal heads, etc., and other photofabrication techniques.
The increasing integrity of LSIs has revealed the resolution limits of conventional single layer resists, and multilayer resist lithography has been proposed to form a thick and yet fine pattern having a high aspect ratio. According to the multilayer resist lithography technique, a thick organic polymer layer (first layer) is formed on a substrate, and a thin resist layer is provided thereon to form a second layer, which is exposed to high energy rays and developed to form a resist pattern. The first layer of the organic polymer is then anisotropically etched by oxygen plasma (O2-RIE) using the resist pattern as a mask thereby to make a pattern with high rectangularity (see Lin, Solid State Technology, 1981, 24, 73).
The above-described two-layer resist process has an advantage that the second resist layer can be applied thin so that the resulting resist pattern is expected to have a high resolution, a high aspect ratio, and a larger depth of focus (DOF). Because the second resist layer must have high resistance to O2-RIE, it is generally formed of a silicon-containing polymer. In particular, many attempts have been directed to use of acid-degradable group-containing vinyl polymers having a silicon atom in the side chain thereof from the standpoint of wide freedom of molecular design and availability or ease of synthesis of starting materials. Such attempts are found, e.g., in JP-B-7-99435, EP494383, and U.S. Pat. Nos. 5,998,557 and 5,856,071.
Nevertheless the studies that have hitherto been given to the two-layer resist process have not succeeded in simultaneously satisfying the requirements of resolution, DOF, and freedom from development defects in ultrafine patterning.
Further, where the state-of-the-art two-layer resist process is applied to fine pattern formation on a silicon wafer using, for example, an ArF laser as an exposure light source at near the resolution limit of 0.14 xcexcm or narrower, the resulting resist pattern has insufficient dimensional uniformity. When it comes to contact hole pattern formation, in particular, variation in shape and size of the contact holes has posed a problem. If a resist pattern has varied dimensions from place to place in a plane, the variation would be transferred to the substrate in etching, resulting in deterioration of electrical characteristics, which leads to a reduced yield.
An object of the present invention is to provide a positive resist composition adapted to be exposed to far ultraviolet rays from an ArF laser or a KrF laser which provides a resist pattern with improved dimensional uniformity and excellent resist characteristics, such as resolution, DOF, and freedom from development defects.
The present inventors have conducted extensive studies paying attention to these performance properties and reached the present invention. The object of the invention is accomplished by:
(1) A positive resist composition comprising (A) a polymer having a silicon atom in the side chain thereof which is insoluble or sparingly soluble in an aqueous alkali solution and becomes soluble in an aqueous alkali solution by the action of an acid and (B) an acid generator capable of generating an acid on exposure to active light rays or a radiation which is represented by formula (I): 
wherein R1, R2, R3, R4, and R5, which are the same or different, each represent a hydrogen atom, a nitro group, a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted alkoxycarbonyl group, a substituted or unsubstituted aryl group or a substituted or unsubstituted acylamino group; at least two of R1, R2, R3, R4, and R5 may be taken together to form a cyclic structure; R6 and R7, which are the same or different, each represent a hydrogen atom, a cyano group, a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group; Y1 and Y2, which are the same or different, each represent a substituted or unsubstituted alkyl group which may contain an ether linkage or a sulfide linkage or a substituted or unsubstituted alkenyl group provided that, when Y1 and Y2 each represent an alkyl group, (i) at least one of them is an alkyl group having a hydroxyl group, an ether linkage or a sulfide linkage or (ii) Y1 and Y2 each represent an alkyl group having two or more carbon atoms; at least one of R1, R2, R3, R4, and R5 and at least one of Y1 and Y2 may be taken together to form a ring; at least one of R1, R2, R3, R4, and R5 and at least one of R6 and R7 may be taken together to form a ring; and the acid generator may consist of two or more structures represented by formula (I) linked up together at any one of R1, R2, R3, R4, R5, R6, and R7 or any one of Y1 and Y2 via a linking group; and Xxe2x88x92 represents a non-nucleophilic anion.
(2) The positive resist composition according to (1), wherein the polymer (A) comprises a repeating unit represented by formula (1): 
wherein R2, R3, and R4 each represent an alkyl group, a haloalkyl group, a halogen atom, an alkoxy group, a trialkylsilyl group or a trialkylsilyloxy group; and n represents 0 or 1, and at least one of a repeating unit represented by formula (2a): 
wherein Y2 represents a hydrogen atom, an alkyl group, a cyano group or a halogen atom; L represents a single bond or a divalent linking group; and Q represents a group capable of generating a carboxylic acid on decomposing by the action of an acid, and a repeating unit represented by formula (2b): 
wherein X1 and X2 each represent an oxygen atom, a sulfur atom, xe2x80x94NHxe2x80x94 or xe2x80x94NHSO2xe2x80x94; L11 and L12 each represent a single bond or a divalent linking group; two A2""s each represent a hydrogen atom, a cyano group, a hydroxyl group, xe2x80x94COOH, xe2x80x94COOR5, xe2x80x94COxe2x80x94NHxe2x80x94R6, a substituted or unsubstituted alkyl group, an alkoxy group or xe2x80x94COOQ; R5 and R6 each represent a substituted or unsubstituted alkyl group; and Q represents a group capable of generating a carboxylic acid on decomposing by the action of an acid.
(3) The positive resist composition according to (1), wherein the polymer (A) comprises a repeating unit represented by formula (1), at least one of repeating units represented by formulae (2a) and (2b), and a repeating unit represented by formula (3): 
wherein Z represents xe2x80x94Oxe2x80x94 or xe2x80x94N(R7)xe2x80x94; R7 represents a hydrogen atom, a hydroxyl group, an alkyl group, a haloalkyl group or xe2x80x94OSOxe2x80x94R8; and R8 represents an alkyl group, a haloalkyl group, a cycloalkyl group or a camphor residue.
(4) The positive resist composition according to (1), wherein the polymer (A) comprises a repeating unit represented by formula (4): 
wherein R0 represents a hydrogen atom, an alkyl group, a cyano group or a halogen atom; L21 represents a divalent, trivalent or tetravalent linking group; R2, R3, and R4 each represent an alkyl group, a haloalkyl group, a halogen atom, an alkoxy group, a trialkylsilyl group or a trialkylsilyloxy group; and 1 represents an integer of 1 to 3.
(5) The positive resist composition according to any one of (1) to (4), wherein the composition further comprises (C) an organic basic compound as an acid scavenger.